1. Field of the Invention
The present invention relates to a method for wafer level packaging, and more particularly, to a method for wafer level packaging having a hermetic window formed by hermetic bonding of cap structures to a device wafer.
2. Description of the Prior Art
Generally, a wafer level package (WLP) is a semiconductor package in which the size of a finished package is similar to or slightly larger than a semiconductor die. After completion of all test processes and assembly processes or packaging processes, individual semiconductor packages are separated from a wafer having a plurality of semiconductor dies. Therefore WLP not only decreases a size of a memory module, but also satisfies a demand for high density. Further, WLP improves transmission speed and stability by effectively reducing noise. Please refer to FIGS. 1-4, which are schematic diagrams illustrating a conventional method of wafer level packaging. As shown in FIG. 1, a device wafer 10 including a plurality of devices 12 positioned on its surface is provided. A dicing process is performed according to predefined scribe lines (not shown) so as to separate the device wafer 10 into a plurality of dies 14.
Please refer to FIG. 2. A cap wafer 20 is provided and undergoes a segmenting process to form a plurality of caps 22. The shape of each cap 22 corresponds to each die 14 while the size of each cap 22 is similar to or slightly smaller than the size of the die 14. Please refer to FIG. 3. A sealing agent 30, such as a polymer glue, is applied to a surface of the die 14. As shown in FIG. 4, the cap 22 is bonded to the die 14 by the sealing agent 30.
When the device wafer carries image sensory devices or microelectromechanical systems (MEMS) devices, which need space for light-sensing areas or allowing the MEMS devices to move, hermetic windows are required to protect the devices from contamination by air, dust, moisture, etc. The hermetic windows also protect the devices from mechanical or radioactive influences, prevent gas, which fills the hermetic window of the image sensory device die, from leaking, and prevent destruction of the vacuum condition of the hermetic window of the MEMS device die. The reliability and lifetime of the die depend on the hermetic window made by the hermetically sealed cavity or protective cap. In addition, the sealing agent used in the conventional method is easily affected by heat and thus affects the reliability of the package, making the sealing agent unsuitable for hermetic packaging.
In addition to the considerations mentioned above surrounding hermetic sealing, the dies are individually and manually bonded to the protective caps and packaged after dicing of the device wafer. Therefore the conventional method reduces the efficiency of back-end-of-line processes and the yield of semiconductor packaging processes or MEMS processes, and suffers the disadvantages of high cost and labor.